In recent years, an amount of information processing is increasing, accompanied by development of a cloud service. In order to process this enormous amount of information, a data center is provided and operated in a plurality of regions. In a data center, electronic devices such as a server and a network device are collectively installed. Thus, energy efficiency of a data center is enhanced.
In an electronic device such as a server and a network device within a data center provided in each region, for example, heat generating components such as a central processing unit (CPU) and a large scale integration (LSI) are accommodated. These heat generating components accompany heat generation. Therefore, in a data center, electronic devices are cooled by using an air conditioner, for example.
However, since an amount of information processing of a data center is increasing, power consumption of an air conditioner is also increasing. Therefore, a running cost of a data center is also increasing. In view of the above, reducing power consumption of an air conditioner in a data center is being demanded.
PTL 1 discloses a technique for reducing power consumption of an air conditioner, as an ambient heat exchange system. In PTL 1, an ambient heat exchange system includes an air cooling heat exchanger 11, a heat exchanger 12, a pump 13, and a control device 30. The air cooling heat exchanger 11 is a heat exchanger installed outdoors. The heat exchanger 12 is a heat exchanger installed indoors. The air cooling heat exchanger 11 includes a heat exchanger body 11a, a fan 11b (air conditioner), and the like. A thermometer 21 measures an intake air temperature of the air cooling heat exchanger 11. A thermometer 22 measures an exhaust air temperature of the air cooling heat exchanger 11. A wattmeter 23 measures power consumed by the pump 13. A wattmeter 24 of the fan 11b measures power consumption of the fan 11b. The control device 30 controls a rotational speed of the fan 11b. 
Further, the control device 30 calculates a heat exchanging amount of the air cooling heat exchanger 11, based on a temperature difference between an intake air temperature and an exhaust air temperature of the air cooling heat exchanger 11, and an amount of airflow from a fan being calculated from a rotational speed of the fan 11b. The control device 30 calculates a coefficient of performance (COP), based on a calculated value of a heat exchanging amount, and power consumption of the pump 13 and the fan 11b. A coefficient of performance is an index indicating cooling ability per unit power consumption. Further, the control device 30 increases or decreases a rotational speed of the fan 11b in such a way as to increase a calculated coefficient of performance.
In this way, in the technique described in PTL 1, an ambient heat exchange system calculates a coefficient of performance (COP), based on a heat exchanging amount with respect to ambient air and power consumption in the ambient heat exchange system, and controls a rotational speed of a fan in the ambient heat exchange system, based on the coefficient of performance (COP). Further, when a coefficient of performance (COP) falls below a predetermined threshold value, the ambient heat exchange system is stopped. Thus, energy saving is performed by performing an operation with maximum efficiency in various ambient conditions.